1. Field of the Invention
The present invention relates to a cleaning device and to an image forming apparatus using the same. In detail, the invention relates to a cleaning device excellent in cleaning performance and durability and to an imaging forming apparatus using the same.
2. Description of the Related Art
A general electrophotographic process includes a step of charging an image carrier such as a photoconductor; a step of forming an electrostatic latent image on the photoconductor by image exposure; a step of developing the electrostatic latent image with a toner to form a toner image; a step of transferring the toner image onto a material to be transferred; and a step of cleaning the residual toner on the photoconductor, and further includes a step of destaticizing the photoconductor as the need arises. In a development step of a dry electrophotographic system, a toner image is formed by using a powdered toner, which is then transferred onto a material to be transferred such as paper and an intermediate transfer medium. The residual toner on the photoconductor after the transfer or the toner which has not been transferred from the photoconductor due to a paper jam or the like is removed from the photoconductor in a subsequent cleaning step by a cleaner such as a blade, a brush applied with a bias, and a roller.
For example, though a blade cleaning system can be configured relatively cheaply, it is insufficient for cleaning a toner which is in general a fine particle; and for the purpose of obtaining a sufficient cleaning performance, when the blade is brought into strong contact with the photoconductor, an edge part of the blade is partially broken, or the blade is turned up. And, when the edge part of the blade is broken or turned up, a cleaning performance set up at the beginning is not obtained, cleaning failure occurs, and a serious defect is generated on an image.
Then, there is taken a countermeasure for widening a margin of a cleaning condition by containing a fluorocarbon resin in a photoconductor surface portion which is a member to be cleaned or mixing a lubricant such as zinc stearate into a toner, thereby reducing the friction between the blade and the photoconductor surface to make the toner easy to peel away from the photoconductor. However, if a large amount of a mold releasing agent is mixed in the photoconductor surface portion, characteristics of the photoconductor must be sacrificed to some extent, and it is difficult to obtain a photoconductor with high performance. Also, if a lubricant is mixed in the toner, a charging performance as the toner is influenced not a few, and it is difficult to obtain a toner with high performance. Also, even when the foregoing countermeasure is taken, it is difficult to make both sufficient cleaning performance and durability compatible with each other.
Also, in addition to the blade cleaning system, for example, a sponge roller is used as a cleaning measure using a roller. This is a system in which an elastic sponge roller constituted of expanded polyurethane or the like is brought into contact with a photoconductor and a toner is moved into a side of the sponge roller by an electric field and is a system in which cleaning is performed while storing the toner in the sponge roller during the image forming action and the toner is discharged out into a side of the photoconductor between papers on which an image is not formed or at the time of finish action or the like, thereby recovering the toner by a development unit or a separately provided cleaner. Separately from this, there is also known a system in which a metallic roller or the like is further brought into contact with a sponge roller and provided with a blade cleaner or the like, thereby recovering the toner.
In the foregoing cleaning measure using a roller, since the electric field is applied by using the sponge roller, a bearing or a bias feed measure is essential. Also, in the foregoing system of once storing the toner in the roller and then discharging out it, a reversely charged toner or the like cannot be controlled, a problem of deterioration of image quality is inevitable, and simultaneously, a discharge-out action or the like must be frequently carried out, whereby the performance of apparatus is lowered. Also, in the system of recovering the toner by providing a metallic roller or the like, parts such as a metallic roller and a blade are additionally needed, the costs are expensive, and the configuration becomes large in size. Furthermore, even in the foregoing systems, when the particle size of the toner is small, sufficient cleaning becomes difficult. Under these circumstances, there are made some attempts to improve the performance of an elastic roller such as a sponge roller.
For example, JP-A-2003-226773 discloses a method of preparing an expanded elastic roller for cleaning by a supercritical fluid technology and results of use thereof. Furthermore, JP-A-2003-231769 discloses a method of preparing expanded polyurethane by employing a supercritical fluid technology, an expanded sponge roller obtained by the subject method and results of use thereof. According to the expanded sponge roller disclosed in JP-A-2003-231769, it is disclosed that a cleaning performance is improved and that a blade can be prepared in the same configuration.
On the other hand, the blade cleaning is advantageous as a cleaning measure because of a relatively cheap device configuration. Then, the present inventors made expanded blades on an experimental basis in the manufacturing methods disclosed in the foregoing patent documents and carried out tests. As a result, they found the following problems.
(i) When the foregoing expanded blade is formed in a pad-like shape and brought in a fixed area into contact with a photoconductor, though the initial cleaning performance is good, cleaning failure occurs immediately due to plugging.
(ii) When an edge part of the foregoing expanded blade is brought into contact with a photoconductor as in usual blades, a good cleaning performance is not obtained from the beginning. Also, when a paper-passing test is carried out, cleaning failure occurs immediately as the case may be.
(iii) As compared with conventional urethane rubbers, the expanded polyurethane is weak in “elasticity” and narrow in a margin of a cleaning condition, and blade turning up is easy to occur overwhelmingly.
As described above, though JP-A-2003-226773 and JP-A-2003-231769 describe that the elastic expanded body prepared by a supercritical fluid technology can be utilized as a cleaning roller or a blade in an electrophotographic apparatus, even when an expanded blade is prepared merely by the technologies disclosed in these patent documents, a sufficient cleaning performance cannot be obtained. Originally, in the case of blade cleaning, when an expanded body is used, it is just like the matter that “blade breakage” appears to occur from the beginning, and a good cleaning performance cannot be expected. Also, as common sense in the art, the “cleaning using an expanded body” as referred to herein is not blade cleaning but means a technology using a cleaning roller or a cleaning pad. Accordingly, there has not hitherto been made a proposal to venture to employ an elastic expanded body for blade cleaning, thereby improving cleaning performance or durability or the like as in the invention.